Commonly used localization approaches developed for mobile vehicle or robot navigation include dead reckoning, GPS, vision systems (both onboard and off-board), baseline navigation, inertial navigation, sonar, and laser point clouds. The principal disadvantages of dead reckoning methods are that navigation errors grow without bound and systems cannot accommodate effector slip. Absolute localization methods, such as those that use GPS, bound error but can often fail in indoor environments due to signal loss. Vision systems, sonar, and laser point clouds use relative information from the environment, but require training to interpret sensor data for use in deliberative robot architectures. Inertial navigation systems rely on integrating accelerations and, like dead reckoning, suffer from unbounded error. Baseline navigation is similar to GPS navigation in that absolute position information is derived from beacons with known absolute position. Although beacons can be placed in areas that would otherwise be GPS-denied, at least two beacons must always remain in line-of-sight to eliminate disambiguates and sensors must be capable of measuring range or bearing to beacons.
Another type of localization utilizes “radio frequency identification” (RFID) tags. RFID localization systems typically employ Received Signal Strength Indication (RSSI) or proximity methods in Cartesian or polar fields. RFID localization approaches based on RSSI use an approximation of time-of-flight of RF signals to deduce range information to fixed RFID tags. This trilateration approach is similar in concept to GPS and baseline navigation. Thus, errors result because the distance-RSSI relationship is extremely non-linear, and the only practical way to use RSSI is through careful calibration of a known environment. However, even with careful calibration, changes within the environment can have a significant impact on RSSI signals (e.g., opening or closing a door or even movements of the robot within the environment) that require a recalibration. RFID localization based on proximity localization utilizes a set of RFID tags with known locations on a floor. Location is determined under the assumption that visible tags are within a given radius of the antenna. In addition, since tags are located on the floor, tags are exposed to damage from robot movement or by other equipment/personnel sharing the space.